Twenty Years On: RECIST as a Biomarker of Response in Solid Tumours an EORTC Imaging Group – ESOI Joint Paper

Response evaluation criteria in solid tumours (RECIST) v1.1 are currently the reference standard for evaluating efficacy of therapies in patients with solid tumours who are included in clinical trials, and they are widely used and accepted by regulatory agencies. This expert statement discusses the principles underlying RECIST, as well as their reproducibility and limitations. While the RECIST framework may not be perfect, the scientific bases for the anticancer drugs that have been approved using a RECIST-based surrogate endpoint remain valid. Importantly, changes in measurement have to meet thresholds defined by RECIST for response classification within thus partly circumventing the problems of measurement variability. The RECIST framework also applies to clinical patients in individual settings even though the relationship between tumour size changes and outcome from cohort studies is not necessarily translatable to individual cases. As reproducibility of RECIST measurements is impacted by reader experience, choice of target lesions and detection/interpretation of new lesions, it can result in patients changing response categories when measurements are near threshold values or if new lesions are missed or incorrectly interpreted. There are several situations where RECIST will fail to evaluate treatment-induced changes correctly; knowledge and understanding of these is crucial for correct interpretation. Also, some patterns of response/progression cannot be correctly documented by RECIST, particularly in relation to organ-site (e.g. bone without associated soft-tissue lesion) and treatment type (e.g. focal therapies). These require specialist reader experience and communication with oncologists to determine the actual impact of the therapy and best evaluation strategy. In such situations, alternative imaging markers for tumour response may be used but the sources of variability of individual imaging techniques need to be known and accounted for. Communication between imaging experts and oncologists regarding the level of confidence in a biomarker is essential for the correct interpretation of a biomarker and its application to clinical decision-making. Though measurement automation is desirable and potentially reduces the variability of results, associated technical difficulties must be overcome, and human adjudications may be required.

Elucidating Macular Structure-Function Correlations in Glaucoma

Correlation between structural data from optical coherence tomography (OCT) and functional data from the visual field (VF) may be suboptimal because of poor mapping of OCT measurement locations to VF test stimuli. We tested the hypothesis that stronger structure-function correlations in the macula can be achieved with fundus-tracking perimetery, by precisely mapping OCT measurements to VF sensitivity at the same location. The conventional 64 superpixel (3°x3°) OCT grid was mapped to VF sensitivities averaged in 40 corresponding VF units with standard automated perimetry (conventional mapped approach, CMA) in 38 glaucoma patients and 10 healthy subjects. Similarly, a 144 superpixel (2°x2°) OCT grid was mapped to each of the 68 VF locations with fundus-tracking perimetry (localized mapped approach, LMA). For each approach, the correlation between sensitivity at each VF unit and OCT superpixel was computed and the maximum value used to generate vector maps. CMA yielded significantly higher structure-function correlations compared to LMA. Only 20% of the vectors with CMA and <5% with LMA were within corresponding mapped OCT superpixels, while most were directed towards loci with structural damage. Measurement variability and patterns of glaucomatous damage are more likely to affect the correlations rather than precise mapping of VF stimuli.

Limitations of Muscle Ultrasound Shear Wave Elastography for Clinical Routine—Positioning and Muscle Selection

Shear wave elastography (SWE) is a clinical ultrasound imaging modality that enables non-invasive estimation of tissue elasticity. However, various methodological factors—such as vendor-specific implementations of SWE, mechanical anisotropy of tissue, varying anatomical position of muscle and changes in elasticity due to passive muscle stretch—can confound muscle SWE measurements and increase their variability. A measurement protocol with a low variability of reference measurements in healthy subjects is desirable to facilitate diagnostic conclusions on an individual-patient level. Here, we present data from 52 healthy volunteers in the areas of: (1) Characterizing different limb and truncal muscles in terms of inter-subject variability of SWE measurements. Superficial muscles with little pennation, such as biceps brachii, exhibit the lowest variability whereas paravertebral muscles show the highest. (2) Comparing two protocols with different limb positioning in a trade-off between examination convenience and SWE measurement variability. Repositioning to achieve low passive extension of each muscle results in the lowest SWE variability. (3) Providing SWE shear wave velocity (SWV) reference values for a specific ultrasound machine/transducer setup (Canon Aplio i800, 18 MHz probe) for a number of muscles and two positioning protocols. We argue that methodological issues limit the current clinical applicability of muscle SWE.

Pan-cancer analysis of the effect of biopsy site on tumor mutational burden observations

Background Tumor mutational burden (TMB) has been proposed as a predictive biomarker of response to immunotherapy. Efforts to standardize TMB scores for use in the clinic and to identify the factors that could impact TMB scores are of high importance. However, the biopsy collection site has not been assessed as a factor that may influence TMB scores. Methods We examine a real-world cohort comprising 137,771 specimens across 47 tissues in 12 indications profiled by the FoundationOne assay (Foundation Medicine, Cambridge, MA) to assess the prevalence of biopsy sites for each indication and their TMB scores distribution. Results We observe a wide variety of biopsy sites from which specimens are sent for genomic testing and show that TMB scores differ in a cancer- and tissue-specific manner. For example, brain or adrenal gland specimens from NSCLC patients show higher TMB scores than local lung specimens (mean difference 3.31 mut/Mb; p < 0.01, 3.90 mut/Mb; p < 0.01, respectively), whereas bone specimens show no difference. Conclusions Our data shed light on the biopsied tissue as a driver of TMB measurement variability in clinical practice.

NIMG-33. VOLUMETRIC TUMOR MEASUREMENTS ARE SUPERIOR TO 2D BIDIRECTIONAL MEASUREMENTS IN THE EVALUATION OF IDH INHIBITION IN DIFFUSE GLIOMAS: EVIDENCE FROM A PROSPECTIVE PHASE I TRIAL OF IVOSIDENIB

Since IDH mutant (mIDH) low-grade gliomas (LGGs) progress slowly and patients have a relatively long survival, testing of new therapies in clinical trials based solely on survival can take more than 20 years. Guidance on therapeutic evaluation using LGG RANO criteria recommends serial bidirectional (2D) measurements on a single slice; however, questions remain as to the best approach for evaluating LGGs in clinical trials including use of volumetric (3D) measurements, which would theoretically allow for more accurate measurements of irregular shaped lesions and allow readers to better assess areas of change within these tumors. A total of 21 (out of 24) non-enhancing, recurrent mIDH LGGs with imaging pre- and post-treatment enrolled in a phase I, multicenter, open-label study to assess the safety and tolerability of oral ivosidenib (NCT02073994) were included in this exploratory ad hoc analysis. 2D bidirectional and 3D volumetric measurements were centrally evaluated by one of 3 radiologists at an imaging CRO using a paired read and forced adjudication paradigm. The effects of 2D vs. 3D measurements on progression-free survival (PFS), growth rate measurement variability, and reader concordance and adjudication rates were then quantified. 3D volumetric measurements had significantly longer estimates of PFS (P=0.0181), more stable (P=0.0063) and considerably lower measures of tumor growth rate (P=0.0037), the highest inter-reader agreement (weighted Kappa=0.7057), and significantly lower reader discordance rates (P=0.0002) with comparable recommended LGG RANO 2D approaches. In summary, 3D volumetric measurements are better for determining response assessment in LGGs due to longer PFS and more stable measures of tumor growth rates (i.e. less “yo-yo-ing” of measurements over time causing fewer erroneous calls of progression and more accurate growth rates), highest inter-reader agreement, and lowest reader discordance rates. Future studies will focus on validating this in a larger cohort and determining whether these measurements better reflect clinical benefit.

Accuracy and Reproducibility of a Software Prototype for Semi-Automated Computer-Aided Volumetry of the solid and subsolid Components of part-solid Pulmonary Nodules

Purpose To test the accuracy and reproducibility of a software prototype for semi-automated computer-aided volumetry (CAV) of part-solid pulmonary nodules (PSN) with separate segmentation of the solid part. Materials and Methods 66 PSNs were retrospectively identified in 34 thin-slice unenhanced chest CTs of 19 patients. CAV was performed by two medical students. Manual volumetry (MV) was carried out by two radiology residents. The reference standard was determined by an experienced radiologist in consensus with one of the residents. Visual assessment of CAV accuracy was performed. Measurement variability between CAV/MV and the reference standard as a measure of accuracy, CAV inter- and intra-rater variability as well as CAV intrascan variability between two recontruction kernels was determined via the Bland-Altman method and intraclass correlation coefficients (ICC). Results Subjectively assessed accuracy of CAV/MV was 77 %/79 %–80 % for the solid part and 67 %/73 %–76 % for the entire nodule. Measurement variability between CAV and the reference standard ranged from –151–117 % for the solid part and –106–54 % for the entire nodule. Interrater variability was –16–16 % for the solid part (ICC 0.998) and –102–65 % for the entire nodule (ICC 0.880). Intra-rater variability was –70–49 % for the solid part (ICC 0.992) and –111–31 % for the entire nodule (ICC 0.929). Intrascan variability between the smooth and the sharp reconstruction kernel was –45–39 % for the solid part and –21–46 % for the entire nodule. Conclusion Although the software prototype delivered satisfactory results when segmentation is evaluated subjectively, quantitative statistical analysis revealed room for improvement especially regarding the segmentation accuracy of the solid part and the reproducibility of measurements of the nodule’s subsolid margins. Key points:

REPRODUCIBILITY OF MEASUREMENTS OF PRE-CONTACT LENS TEAR FILM KINETICS UNDER NORMAL AND ADVERSE ENVIRONMENTAL CONDITIONS

Objectives: To evaluate the reproducibility of tear film kinetics (TFK) measurements during the full interblink period in habitual wearers of delefilcon A daily disposable contact lenses under different environmentalconditions.Methods: Two independent studies were performed, one involving 90 eyes measurements in 49 subjects and the second involving 58 eyes measurements in 32 subjects, after 3 hours of conventional wear in normal environmental conditions (NEC) and an additional 3 hours of computer use under adverse environmental conditions (AEC), defined as 20% relative humidity (RH). Digital videos were obtained by non-invasive Tearscope illumination, followed by a parallel-group post-hoc comparative analysis by masked investigators of the videos obtained during the two studies. Parameters analyzed included non-invasive break-up time (NIBUT); dehydration speed (DS) between the initial break and the spontaneous blink, and minimum protected area (MPA) of the lens surface by the tear film.Results: After 3 hours of wear in normal environmental conditions, the overall population (n=148) had a mean NIBUT of 7.1 ± 7.0 sec, a mean DS of 0.28 ± 0.66 mm2/sec, and a mean MPA of 93.4 ± 16.6%. After an additional 3 hours in AEC, mean NIBUT was 8.4 ± 9.8 mm2/sec, mean DS was 0.26 ± 0.75 mm2/sec, and MPA was 95.2 ± 14.0%. The TFK characteristics in the two studies were similar for each environmental condition: after 3 hours of conventional wear, the mean [95% CI] differences between the two studies were −0.9 [−3.2, +1.4] sec for NIBUT, 0.00 [−0.22, +0.22] mm2/s for DS, and 2.0 [−3.5, +7.4] % for MPA; after an additional 3 hours of wear in 20% RH, the mean [95% CI] differences between the two studies were −1.3 [−4.5, +1.9] sec for NIBUT, −0.03 [−0.28, +0.22] mm2/s for DS and −0.3 [−4.9, +4.3] % for MPA. Conclusions: This analysis showed that the measurement of pre-contact lens TFK carried out in two differ-ent studies involving habitual wearers of delefilcon A having worn their contact lenses for an initial 3 hours under NEC and a further 3 hours under low (20%) hygrometry (AEC) produced similar on-eye wettability, including a long NIBUT, slow DS following the initial break, and wide MPA at the next blink. The results establish the reproducibility of the measurement of pre-contact lens TFK using the Tearscope; by quantifying the measurement variability, the data makes it possible to carry out precise sample size calculations in future studies involving pre-contact lens TFK measurements to quantify on-eye wettability under both normal and adverse environmental low (20% RH) hygrometric conditions.

Laser Doppler Measurements of Systolic Blood Pressure on the First and Second Toe in Patients with Peripheral Arterial Disease

Laser Doppler was used to measure toe blood pressure (TBP) in 40 consecutive patients with various degree of peripheral arterial disease. The aim of this methodological study was to increase the usefulness of TBP by exploring the interchangeability between TBP from the first and second toe and by investigating daily routine reproducibility and measurement variability. According to our study design pressure values were based on three measurements that were averaged. At simultaneous measurements, TBP of the first toe was 71 mm Hg (standard deviation [SD] 25) compared with 70 mm Hg (SD 25) on the second toe. The correlation (r) between first and second toe pressure measurements was 0.84 and intraclass correlation coefficient (ICC) was 0.84. The difference between TBP on the first and second toe was not related to gender, diabetes, or magnitude of the pressures. Repeated TBP measurements of the right first toe after disconnection of cuffs, 5 to 10 minutes rest, and reconnection of cuffs had a coefficient of variation (CV) of 9% and an ICC of 0.93. CV for toe-brachial index (TBI) was 8%. Our results show that measurements of TBP from the second toe to a large extent are interchangeable with those assessed from the first toe and can be used in clinical situations where measurements from the first toe are not feasible. Flow detection with three averaged laser Doppler measurements generates TBP and TBI with low variability.

Quantitative accuracy and precision in multiplexed single-cell proteomics

Single-cell proteomics workflows have considerably improved in sensitivity and reproducibility to characterize yet unknown biological phenomena. With the emergence of multiplexed single-cell proteomics, studies increasingly present single-cell measurements in conjunction with an abundant congruent carrier to improve precursor selection and enhance identifications. While these extreme carrier spikes are often >100-times more abundant than the investigated samples, undoubtedly the total ion current increases, but quantitative accuracy possibly is affected. We here focus on narrowly titrated carrier spikes (i.e., <20x) and assess their elimination for comparable sensitivity at superior accuracy. We find that subtle changes in the carrier ratio can severely impact measurement variability and describe alternative multiplexing strategies to evaluate data quality. Lastly, we demonstrate elevated replicate overlap while preserving acquisition throughput at improved quantitative accuracy with DIA-TMT and discuss optimized experimental designs for multiplexed proteomics of trace samples. This comprehensive benchmarking gives an overview of currently available techniques and guides conceptualizing the optimal single-cell proteomics experiment.